The 63-year-old, who police say was the alleged mastermind of the killings, was initially arrested after CCTV showed him entering the couple’s gated property and leaving in their new white Ford Ranger.

The remains of Alan Hogg and his wife, Nott, were found in a shallow grave on their Thailand property near a river. (AAP)

The truck was then sold to a Lao businessman the day after the couple was reported missing.

Mr Warut was charged with theft but denied any involvement in their disappearance and was released on a $4,360 bail.

The bodies of Mr Hogg and Ms Suddaen were found near a river within the grounds of their home, after the two suspects in custody revealed where they had been buried.

"We have found the bodies of the couple, they are buried by the canal," Thai Police Major General Sanpat Prabpudsa told The Telegraph.

Police had held grave fears for their welfare after a search of the property revealed bloodstains found in a sink and on the wall of their swimming pool changing room.

The couple frequently travelled to Australia, where Mr Hogg worked as an engineer. Locals in their home town of Phrae, in northern Thailand, had described Mr Hogg as a "millionaire".

Their daughter Robyn, 31, travelled to Thailand from the UK when her parents were reported missing by a friend last Thursday.